The present invention is related to spark-ignited internal combustion engine control and the coordination of fuel delivery and spark events in an internal combustion engine employing a distributorless ignition system and sequential fuel delivery system. More particularly, the invention is directed toward developing a signal indicative of absolute engine position in a sequentially fueled, distributorless ignition, internal combustion engine.
In sequentially fueled internal combustion engines, it is necessary to synchronize the fuel charge delivery with the combustion sequence of the engine such that fuel is delivered to an appropriate cylinder at and appropriate time (i.e. to the next cylinder undergoing compression). One manner of accomplishing this task is through the utilization of camshaft sensors which read the rotational position of a camshaft via interaction with a stationary sensing element, for example a variable reluctance or hall effect sensor. Camshaft sensorless methods and apparatus are also known which displace the requirement for this additional hardware by electronically sensing various characteristics of spark events within combustion cylinders and determining therefrom the absolute engine position for use in the synchronization of fueling. Such apparatus tend to be relatively complicated and may be sensitive to cross-talk from other combustion cylinder spark events or other sources of noise induced upon the ignition system.
One such example of a camshaft sensorless system is shown in U.S. Pat. No. 4,543,936 to Gardner et al. and assigned to General Motors Corporation. In that reference, an apparatus is shown having two voltage sense lines capacitively coupled to ends of the secondary winding of an ignition coil. Each end of the secondary winding supplies a respective spark plug in a respective one of a pair of combustion sequence phase-opposed cylinders. That is to say, one of the pair of cylinders reaches top dead center of its stroke in compression phase as the other of the pair of cylinders reaches top dead center of its stroke in exhaust phase. Generally, the spark plug disposed within the cylinder under compression will discharge at a higher voltage than the spark plug disposed within the cylinder under exhaust. The voltage sense lines are coupled to respective inputs of a comparator for differential processing after a predetermined time from initiation of a spark timing event for the cylinder pair. When the voltage on a predetermined one of the voltage sense lines exceeds the voltage on the other, a single sync pulse is generated by cooperation of the comparator and a monostable multivibrator. However, the opposite is not true and no sync pulse is generated when the voltage on the other voltage sense line exceeds the voltage on the predetermined one of the voltage sense line. Therefore, the apparatus provides a single sync pulse indicative of compression in only one of the pair of combustion phase-opposed cylinders.
Another example of such a system is shown in U.S. Pat. No. 5,410,253 to Evans et al., also assigned to General Motors Corporation. In this reference, an apparatus is shown wherein a single voltage sense line is capacitively coupled to both ends of the secondary winding of an ignition coil. The ignition coil again services a pair of spark plugs, each disposed within a respective cylinder of a combustion phase-opposed cylinder pair. Here, the single voltage sense line is branched to independent comparators for detecting voltage transients of a particular phase. The larger transient associated with the cylinder undergoing compression as well as the smaller transient associated with the cylinder undergoing exhaust are both detected. When the transients occur in a certain order and meet a very narrow timing separation constraint (e.g. 1.5 microseconds), a signal indicating compression in a predetermined one of the cylinders is generated. Again, the opposite is not true and compression detection is limited to only the predetermined one of the combustion sequence phase-opposed cylinders.
Therefore, it can be appreciated that the resolution of any such system is as limited as can be in that only one of the two cylinders in a combustion sequence phase-opposed pair is detected. Furthermore, the apparatus shown in Evans et al. is processing transient signals in a time frame positively correlated to undesirable electrical noise making it difficult to adequately attenuate the noise without degrading desirable performance of the apparatus.